A number of electronic oil level control systems for refrigeration compressors have been in use in the past. U.S. Pat. No. 5,103,648 discloses an optical system for monitoring and reacting to oil level within a compressor.
U.S. Pat. No. 6,125,642 teaches an oil level control system employing the complex permittivity of the oil compared with the permittivity of the vapor refrigerant environment.
U.S. Pat. No. 5,911,289 (Clive Waller) discloses an oil level monitoring and control systems based on the use of a float residing on the pool oil surface. The float is attached to one end of a pivoting rod. The rod bears at its other end a permanent magnet that moves in a reverse direction from the float level. The pivoting float, rod and magnet are within the refrigerant/oil circuit. At times the magnet is immersed within the oil pool. The position of the magnet is monitored external of the refrigerant/oil circuit thru a non-ferrous wall built into the device adjacent which the magnet moves. A Hall-Effect magnetic field detector is positioned external of the refrigerant/oil circuit and adjacent the magnetically permeable non-ferrous wall. As the float arm pivots, the arcuate motion of the permanent magnet adjacent the permeable wall causes the Hall-Effect device to respond the change in the strength of the magnetic field associated with the movement of the magnet and thereby activate control valves or alarm signals as required.
All these control devices and systems based on their use have exhibited control problems and false alarms generated during the oil foaming conditions frequently arising during periods of operation immediately after compressor startup or during periods of refrigerant liquid floodback into the oil pool whose level was the control objective.
New non-ozone damaging refrigerants are frequently of the hydrofluorocarbon type (HFC). The manufacturers of these HFC refrigerants require the use of a miscible lubricant such as polyolester (POE). POE acts as a cleaning agent of all the sludge in the system and entrains this dirt with the POE as it returns to the compressor. Not only do the metal particles, accompanying and part of the sludge, accumulate on magnets immersed in the oil, the sludge accumulation can also affect the optical level sensing devices by fostering the formation of surface foam that fools the optical detectors. Foam also occurs when refrigerant dissolved in the oil then boils out of the oil on a sharp reduction of pressure that occurs at starting and other times. Surface foam affects both optical and wave-based sensing systems.
Operational problems with the Waller construction have been reported. These problems have been primarily caused by the weight of very fine metal and iron wear particles in the oil that are attracted to the magnet on one end of the float. As the weight of the Waller magnet gradually increases because of the accretion of the wear particles, the position of the magnet is biased downward, thereby falsely indicating a higher oil level than truly exists, thus failing to cause entry of make-up oil or failing to actuate an alarm, even when the true oil level has dropped to the danger point.
The invention disclosed herein overcomes the faults of the Waller device and the several optical based level sensors and controllers.
It is an object of the invention to provide a liquid level sensing and control device that is unaffected by magnetic and metallic particles.
It is a further object to provide such a device that does not require a magnet positioned within the liquid whose level is sensed.
It is a further object to provide such a device that employs the Hall Effect principle to detect the position of a float positioned to follow level changes of the monitored liquid and to employ as tell-tale an unmagnetized ferromagnetic tell-tale mounted on the float.
It is a further object to provide such a device that employs a float that moves in a straight-line motion in conformance with the change in the level of the monitored liquid.
It is a further object to secure the straight line float motion by providing a float whose motion is constrained by at least one substantially straight guide.
It is a further object to secure the straight line motion by employing a float whose motion is constrained by two substantially straight guides.
It is a further object to provide such straight line motion by employing substantially straight guide members that traverse the float.
It is a further object to facilitate the performance of a Hall Effect sensor by employing a magnet positioned substantially adjacent the Hall Effect sensor.
It is a further object to employ a magnet in the shape of a ring shaped to allow the Hall Effect sensor to occupy a position within the central area of the ring.
It is a further object to moderate the effect of the magnet by the use of a ferromagnetic bridge between the magnet and the working area.
It is a further object to moderate the effect of the ring magnet by employing a ferromagnetic pole-piece positioned in contact with the ring magnet.
It is a further object to moderate the effect of the magnet by employing a ring-shaped pole-piece positioned in substantial contact with the ring magnet.
It is further object to moderate the effect of the magnet by utilizing an electromagnet and moderating the current flow through its windings.
For a closed system, a level sensing and controlling device for a liquid having a rising and falling level, the device including a float of non-magnetic material, a magnetic couple comprising a magnetized part and an unmagnetized part, the float having attached thereto one part of the magnetic couple, at least one guide constraining the float and its attached part to move in a straight substantially vertical line with the rise and fall of the liquid level, a magnetically permeable partition substantially adjacent the float for separating the interior of the closed system from the exterior, a Hall Effect sensor positioned substantially adjacent the partition exterior and the other part of the couple positioned substantially adjacent the Hall Effect sensor.